This invention relates to a TV Sync Generator system in which ROMs (read only memories) are used to determine the timings of the various output pulses and more particularly to a method of conserving memory required in the ROMs.
U.S. Patent Application Ser. No. 169,680 filed July 17, 1980 in the name of T. R. Smith and F. J. Marlowe, now U.S. Pat. No. 4,316,219, and assigned to the assignee of the present invention discloses a television synchronizing circuit that uses two counters respectively reading two ROMs to synthesize the horizontal and vertical synchronizing signals respectively. The clock period for the vertical ROM is one half-line interval, and the basic counted interval is one field. In NTSC and PAL M systems the field interval is 525 half-lines; in PAL B and SECAM systems it is 625 half-lines. Consequently, in the above mentioned application, the minimum number of addresses required in the vertical ROM is 525 or 625, respectively. Further, a particular design for a 525 or 625 line camera requires six output lines. In particular they are: one output to establish the gating of equalizing pulses, one for a vertical cursor signal used to establish a center area for automatic white balance, one for vertical drive, one for a signal called "advanced vertical" used in
to establish a four field sequence, one for vertical blanking, and finally an internal vertical reset pulse to reset the vertical counter after 525 or 625 lines.
If the generator is to be used in a portable camera which is battery operated, then the power consumption of the ROM becomes an important factor. Therefore a CMOS (complementary metal oxide semiconductor) ROM could be used for low power consumption. Further, the ROM should be an EPROM (erasable programmable read only memory) to allow use with either
or NTSC by reprogramming, and to allow for different vertical blanking intervals within one standard at the option of the user.
Commercially available EPROMs come with a number of addresses which number is a power of 2, and the smallest power-of-2 number useable is 1024. A suitable CMOS device with 1024 addresses is type No. IM6653 made by Intersil Inc. However, it has only 4 output lines (1024.times.4 bits). As explained above, the sync generator design for a 525 or 625 line camera requires six output lines. This means that two of said devices would be required for the vertical ROM, thereby increasing the cost, power and required space. Another possibility is to try to use a single device, such as the Intersil IM6654, which has 512 address and 8 output lines. This is more than adequate in number of output lines, but insufficient in number of addresses.
It is desirable to provide a television synchronization generator that has low space, cost and power consumption and is adaptable to different standards. More particularly, to provide such objectives with a synchronization generator having a single 512 address vertical ROM.